Spatial variations of field polarization and phase in microwave cavities: application to the cesium fountain cavity

Wall losses in microwave cavities induce spatial phase variations in all held components. These variations depend on the component and can often be studied separately for each component by the use of suitable transmission line models. By a complete electromagnetic approach the phase relation between different components can be easily found, along with spatial variations, and it can be pointed out that in the presence of losses the vector field polarization is no longer linear, but becomes elliptic and point dependent. In this paper this new way of looking at the effects of wall losses in metal cavities is discussed, as it may become relevant in the context of the study of cavities for atomic frequency standards. In fact, circularly polarized fields can excite different atomic transitions than linearly polarized ones. Another detail which can be studied by electromagnetic calculations, as opposed to transmission line models, is the localized effect of the source on phase and polarization in the neighbourhood of the feed. Useful approaches to this more complex problem are outlined in this paper, and preliminary results are given for the case of a cylindrical TE/sub 011/ cavity, recommended for use in a cesium fountain frequency standard.<>